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Hydraulic heterogeneity and its impact on kinematic porosity in Swedish coastal terrains
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.ORCID iD: 0000-0002-9431-753X
KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Water and Environmental Engineering.
2018 (English)In: Engineering Geology, ISSN 0013-7952, E-ISSN 1872-6917, Vol. 245Article in journal (Refereed) Published
Abstract [en]

Hydrogeology in crystalline rock aquifers is often problematic due to the heterogeneity and anisotropy in thefracture network. Kinematic porosity of the host rock is exceedingly important for municipal decision makers inassessing sustainably extractable water supply volumes and assessing contaminant transport behavior within thematrix. This study explores heteroscedasticity in the hydrogeological characteristics of the fracture network andestimation of kinematic porosity from superficial fracture measurements. Estimates were based on the geometricalproperties of the fractures including: fracture frequency, aperture and orientation. The estimates wereadjusted for aperture changes with depth, connectivity of the fracture network, fracture continuity and measurementorientation bias. The results were compared with well archive data and correlations were found to besignificant with more than 95% confidence. Erratic behaviour of well data relative to fracture measurementsindicates that well orientation with respect to the fracture network gives incomplete hydrogeological data.Spatial heterogeneity of the bedrock was examined using spatial statistics and geographic information systems.The results from the spatial statistical analyses of well data showed that the heterogeneity within the bedrock issufficiently high that spatial correlations cease to exist in nearly all investigated rock types at distances greaterthan 500 m, and in some rocks, particularly sedimentary gneisses, no spatial correlations were observed.Arbitrarily grouped samples with similar geology and topography showed evidence of non-stationary variance.Results indicate that regional generalizations based on sparse point measurements are highly error prone andpotential exists in complementary field-based estimates.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 245
National Category
Environmental Engineering Water Engineering
Identifiers
URN: urn:nbn:se:kth:diva-246195DOI: 10.1016/j.enggeo.2018.08.008ISI: 000448494600006Scopus ID: 2-s2.0-85051820071OAI: oai:DiVA.org:kth-246195DiVA, id: diva2:1296463
Funder
The Geological Survey of Sweden (SGU), 60-1640/2007Swedish Research Council Formas, 2017-01504
Note

QC 20190318

Available from: 2019-03-15 Created: 2019-03-15 Last updated: 2019-08-29Bibliographically approved
In thesis
1. Groundwater resources in hard rock coastal terrains: Insights into heterogeneity and spatial variability
Open this publication in new window or tab >>Groundwater resources in hard rock coastal terrains: Insights into heterogeneity and spatial variability
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Challenges regarding water security in hard rock coastal regions with limited soil cover are: a seasonal absence of recharge during times of peak residency, heterogeneity and variability of the fracture network, close proximity to saline water sources and spatially inconsistent storage and extraction. In areas where it is not feasible to connect residents to municipal water systems, a better understanding of the resilience of reservoirs is needed. The purpose of this study is to investigate and describe the spatial nature of hydraulic data in these types of terrains and present several novel GIS-based groundwater tools with the intent of increasing local water security and aiding in sustainable water resources management. Methods used in this study include groundwater balance modelling and conceptual groundwater storage modelling, as well as a combination of parametric and non-parametric statistical methods such as ANOVA, PCA, correlation and semivariogram analyses. Specific capacity estimates from the Geological Survey of Sweden’s well archive grouped by age or rock type showed very little autocorrelation and in assumed homogeneous geological regions showed statistically significant differences when arbitrarily grouped along a lineament. Estimates of kinematic porosity based on surface fracture data were found have statistically significant correlations with the well data. A GIS-based multivariate prediction tool for assessing Groundwater Resources Potential (GRP) was found to have statistically significant correlations with well data. The GRP method was then combined with a conceptual groundwater storage model and was subsequently found to have statistically significant correlations with chloride concentrations in well quality tests. The storage model was found to have a spatially-dependent sensitivity, meaning that different assumptions within the model had varying effects on the model depending on the geological settings. Incorporating the storage model into a spatial groundwater balance model was then compared with groundwater level time series data over a period of two years, where it was found to have a good explanative capacity and RMSE values of the storage ratio (0.06 to 0.34). Additionally, a soil depth model was developed, tested and found to produce promising results in regions with frequent rock outcrops, where up to 86% of estimates were within 2 m of actual soil depths. Conclusions from this study illustrate the need for a spatial approach to groundwater resources in these types of terrains, and demonstrate a strong potential of several new tools for quantity, capacity and vulnerability estimates to increase water security in a changing climate.

Abstract [sv]

Utmaningar för grundvattenförsörjning i kustnära områden med litet jordtäcke inkluderar begränsad grundvattenbildning under sommarsäsongen när behoven av vatten är som störst, heterogenitet i vattenflöde, närhet till saltvattenkällor samt heterogen lagring och uttag. I områden där det inte är möjligt att ansluta boende till kommunala VA-system behövs en bättre förståelse av magasinens uthållighet för att tillgodose vattenbehoven under nuvarande och ändrade klimatförhållanden. Syftet med forskningen har varit att undersöka det rumsliga beteendet hos hydraulisk data och att öka kunskapen om grundvattnets sårbarhet i kustnära områden med kristallin berggrund och tunna jordlager samt att utveckla verktyg för att beräkna vattenuttag och användning i dylika områden. Projekten har bedrivits med hjälp av GIS-verktyg, parametriska och icke-parametriska statistiska metoder såsom ANOVA, PCA, variogramsanalyser och korrelationsanalyser, samt modellering med grundvattenbalanser och grundvattenlagring.

Brunnsdata från borrade brunnar, grupperade efter ålder och berggrundstyp visade på svag rumslig korrelation. I områden med en antagen geologisk homogenitet hittades statistiskt signifikanta skillnader i brunnkapacitetsdata vid slumpmässig gruppering längs ett lineament. Uppskattningar av kinematisk porositet baserad på ytliga sprickmätningar har visat statistiskt signifikanta korrelationer med brunnskapacitet. Ett multivariat prediktionsverktyg (GRP) för bedömning av områden med god utvinningskapacitet har utvecklats och visade statistiskt signifikanta korrelationer med kapaciteten från existerande brunnar.

GRP-metoden kombinerades sedan med en konceptuell grundvattenmagasinsmodell som visade statistiskt signifikanta korrelationer med kloridhalter tagna från ett brunnskemiarkiv. Magasinsmodellen visade sig ha en rumsligt beroende känslighet, vilket innebar att olika antaganden inom modellen, bland annat avseende geologiska egenskaper i terrängen, hade varierande effekt på modellresultaten. En grundvattenbalansmodell har också utvecklats i GIS och jämförts med verkliga tidserier av grundvattennivå över en tvåårsperiod, med RMSE-värden varierande mellan 0,06 till 0,34. Som hjälp för att beräkna magasineringen i jordlager har en jorddjupsmodell utvecklats och testats vilken visade god överensstämmelse med existerande borrhål i områden med kristallint berg och stor berghällfrekvens.

Slutsatserna från dessa studier ger stöd till behovet av att ta hänsyn till det rumsliga förhållandet hos grundvattenresurserna i områden med kristallin berggrund och visar hur den rumsliga variationen kan beskrivas. Ökad kunskap om den rumsliga variationen kan ge möjlighet att utveckla förbättrade uppskattningar av grundvattenresurserna vilket i sin tur kan leda till bättre användning av befintliga vattenresurser. Dessutom har ett flertal nya verktyg utvecklats för potentiella beräkningar av kvantitet, kapacitet och sårbarhetsanalyser för grundvattenresurserna vilka kan användas för att analysera vattensäkerheten vid olika klimat- och markanvändningsscenarier.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 45
Series
TRITA-ABE-DLT ; 1932
Keywords
Crystalline Rock, Groundwater Balance, Kinematic porosity, Groundwater Recharge, Water Security, Coastal Aquifer
National Category
Water Engineering Environmental Management Environmental Sciences
Research subject
Land and Water Resources Engineering
Identifiers
urn:nbn:se:kth:diva-256317 (URN)978-91-7873-272-2 (ISBN)
Public defence
2019-09-20, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
The Geological Survey of Sweden (SGU), 60-1640/2007Swedish Research Council Formas, 2017-01504
Note

QC 20190830

Available from: 2019-08-30 Created: 2019-08-29 Last updated: 2019-08-30Bibliographically approved

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